This disclosure relates generally to the field of electric motors and generators, and to methods and apparatus for cooling such. For example, the disclosure discusses a technique for dissipating heat in motors and generators by routing fluid along internal surfaces of a stator core. Although the present discussion focuses on electric motors and generators, the present invention affords benefits to a number of applications related to lamination stacks and to the cooling of such stacks.
During operation, conventional motors and generators generate heat. Indeed, the physical interaction of the devices various moving components produces heat by way of friction. Additionally, the electromagnetic relationships between the stator and the rotor produce currents that, in turn, generate heat due to resistive heating, for example. As yet another source of heat, AC magnetic fields lead to losses in the magnetic steel supporting the windings and conductors in the stator and rotor, respectively. The heat is removed by the motor cooling system.
The main magnetic path in an electric motor or generator is generally through the magnetic material that supports the stator or rotor conductors. This magnetic material makes up the stator and rotor core. To reduce magnetic flux produced losses, which generate heat, the magnetic core is laminated, with the lamination plane being in the same plane as the direction of the main magnetic flux path. In conventional radial air gap motors and generators, the stator and rotor core are, therefore, constructed from laminations that are assembled into an axial stack (i.e., a lamination stack).
The exemplary laminations are supported in a frame and cooperate with one another to form a lamination stack. Each exemplary lamination comprises a central aperture sized to receive a rotor, and a plurality of slots disposed circumferentially about the central aperture. These slots are configured to receive a plurality of windings. As will be described in greater detail below, additional apertures may be made in the laminations, and the laminations may be stacked in such a way, that the cooperation of the apertures in adjacent laminations forms a heat exchanger with relatively large axial channels, and relatively small angular channels, connecting the axial channels. The relatively large axial channels will be referred to as manifolds, while the relatively small angular channels will be referred to as micro-channels. The micro-channels extend through the stator core as they are formed by cooperation between appropriately configured apertures located within the stator lamination. The manifolds extend longitudinally through the stator lamination stack and radially inboard of the outer peripheral surface of the stack. The width of the micro-channels may be equal to the lamination thickness or a multiple of the lamination thickness (e.g., twice the lamination thickness); the proper choice of the micro-channel width depends on the specific design.
The arrangement of lamination stacks may create supply and discharge manifolds. The supply manifold may feed two adjacent discharge manifolds, and the discharge manifold may collect the coolant from two adjacent supply manifolds. With a proper choice of the dimensions, the flow in all micro-channels may essentially be the same. The cooling may mainly occur in the micro-channels. The coolant may enter the micro-channels at a temperature corresponding essentially to the overall stator coolant inlet temperature. As the coolant in the micro-channel warms up, it may leave the micro-channels at a temperature corresponding essentially to the overall stator coolant outlet temperature. A header may distribute the colder inlet flow into the supply manifolds and collect the hotter outlet flow from the discharge manifolds. The coolant flow pattern in the manifolds may be arranged to form a counter-flow heat exchanger or a parallel flow heat exchanger.
Accordingly, by routing fluid through the micro-channel heat exchanger formed in the stator, a mechanism for cooling the radially outward regions of the lamination stack that forms the stator is provided. Advantageously, the surface area of the micro-channel heat exchanger may be 1-2 orders of magnitude larger than the outer surface of the motor. Additionally, the small width of the micro-channels results in high value of the film coefficient. Additionally, the split of the total flow into a very large number of parallel streams decreases the pressure required to drive the flow through the heat exchanger. As a result, a highly efficient heat exchanger is integrated into the lamination stack.